Hybrid coil

A hybrid circuit is used in telecommunications to couple a four-wire line with a two-wire line, and vice versa, thus enabling an undisturbed approximation in signal transmission in both directions over a two-wire cable. Is a directional coupler for the low frequency.

The hybrid circuit is a simple form of an echo canceller, in which the transmitted signal, after appropriate filtering ( line simulation or echo estimate signal ) received from the duplex signal to a differential transformer (DT) is " subtracted " is.

It is located for example in analog telephones as so-called Rückhördämpfungsschaltung and enables simultaneous listening and speaking via a single pair of wires, without the speaker himself listening to loud in the telephone receiver.

Applications

Sidetone

In left figure is the hybrid circuit, as is used in analog telephones in the fixed network using mapped. The coming of the left connection line is simulated by the right denoted by Z network. This transmission line model represents the characteristic impedance of the cable, which is complex in some kHz and is formed of resistors and capacitors. Depending on the length of the components used are adapted to their values. The signal from the microphone M (low impedance) is transferred in equal parts on both the cable and over the line model at the primary side of the transformer DT with Mittelpunktanzapfung. The contrary motion of the microphone alternating current in the two primary windings, the signal clears up by the microphone from the secondary winding of the transformer in the ideal case and is not output from the speaker L. The signal from the remote site, however, passes through the connecting cable through the past for this signal direction in series primary windings of the transformer and DT line simulation for speaker L ( high impedance) and is issued there. Thus, the own sound signal from the microphone is suppressed in the speaker while the audio signal from the peer is only slightly dampened by the hybrid circuit in the speaker. However, in telephone sets is not the sidetone ideal (ie infinite) be, since then the speaker the impression of a "dead" line is created. A degree eigenener language in the telephone receiver is intentional.

Analog transmission system

Hybrids were important components in the analog transmission system. Due to the attenuation of the signal had to be inserted at regular intervals into the amplifier lines. But since amplifiers operate in only one direction, had before being amplified on a two-wire line via a hybrid circuit, the call directions are separated and brought together again behind the amplifier. The signal separation of two-to four-wire line never completely successful, since the adjustment of the transmission line model does not perfectly match. A small proportion of the signal always enters the return channel and is then heard as an echo at the station. For this reason, the number of the " forks " in a trunk line is limited; remote connections were therefore performed four-wire between the exchanges, even if the more wires were needed in practice.

Broadcasting

When listeners call in to radio broadcasts and are switched "live", they must turn off their radio receivers to avoid feedback; they hear the broadcast then over the phone. Particularly efficient, finely tuned or digitally running hybrid circuits ( due to the mix of two- and four-wire systems, also referred to as a telephone hybrid ) then result in a two-wire line ("speaking" ), which is connected to the mixer for the show, and another ("listening " ), via which the transmitted audio signal is played to the caller. As well as the volume of the caller may be adjusted without affecting the signal played back.

NT

In the NT the ISDN Basic Rate Interface, a hybrid circuit is included that converts the digital signals of the two-wire line via the UK0 interface to and from the switch to the four-wire S0 bus inside the house.

Here, the transmission line model is adaptive due to the higher requirements for echo cancellation, that is, it adjusts automatically to the existing line.

Properties

Wherein the hybrid circuit, the half of the own transmission power in the transmission line model is lost, i.e., it takes twice the transmit power for the same range and has the same transmission power of a corresponding lower range with respect to the four-wire line with a separate pair of wires for each direction.

• Communication technology
• Transmission technology
• Electrical circuit